refactor: fold org-template's action lifecycle + pendingPublish into one union (RD-13)

Before this change, org-template.store.ts held the action lifecycle in an
actionState signal and the publish impact-confirm gate in an independent
pendingPublish signal. The two were representable in combination, so
pendingPublish === true and busy === true could both hold at once. That
state was meaningless: the UI would show the publish-impact confirmation
while a publish was already in flight.

OrgTemplateState.Loaded now carries one action field, a four-variant union
(Idle | ConfirmingPublish | Busy | Failed). ActionStarted overwrites the
field straight to Busy from any prior tag, so ConfirmingPublish and Busy
can never coexist — not by convention, but because one field can only
hold one tag. requestPublish and cancelPublish become dispatches
(PublishRequested/PublishCancelled); as the reducer already no-ops
outside Loaded, this changes no behaviour. The other four commands
(confirmPublish, rollback, proefbrief, flushSave) keep their existing
loaded() guards. busy, lastError and pendingPublish stay on the store as
computed values reading the new union, with byte-identical public
signatures — no file under brief/ui/ changes.

Ran gen:behaviour-spec for the six new reducer cases.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

libs/shared/docs/behaviour-spec.mdx

@@ -20,7 +20,7 @@ tested where._
 
 Every bullet below is a real test name from the suite — an `it()` title (frontend) or a test
 method name (backend), read as a sentence. Nothing here is hand-written prose: this page
-**is** the suite, reshaped for a business reader. 524 frontend behaviours across
+**is** the suite, reshaped for a business reader. 530 frontend behaviours across
 9 contexts; 261 backend behaviours across 42 test
 classes.
 
@@ -308,6 +308,12 @@ classes.
 - a completed logo upload sets logoDocumentId + dirty
 - removing the logo clears logoDocumentId + dirty
 - DraftLoaded (sub-org switch) keeps the loaded logo category, drops uploads
+- PublishRequested moves a loaded template to ConfirmingPublish
+- PublishCancelled returns to Idle
+- ActionStarted from ConfirmingPublish goes to Busy, so confirming and busy cannot coexist
+- ActionFailed carries the error
+- DraftLoaded resets a stale action error to Idle
+- an action message is a no-op when the template is not loaded
 
 #### parseOrgTemplateAdminView